1. Technical Field
The invention relates to a rotatable gripping device designed for machining or transport of a part with an arbitrary geometry.
In particular, this type of device can be used on a universal table for gripping one or several parts during machining or transport. In particular, it can be used for gripping parts with a wide variety of geometries with different complexities.
2. State of the Art
As illustrated particularly in document FR-A-2 700 487, it is known how to transport parts between different stations in an industrial installation making use of a transport pallet comprising a horizontal support plate equipped with an inner chamber forming a vacuum reservoir. Holes arranged in a regular network penetrate through the upper face of the support plate and open up into the inner chamber. Depending on the shape and dimensions of the parts to be transported, each hole contains either a gripping device with a suction cup, or a positioning device, or a closer. Each gripping device comprises a vertical column with a gripping suction cup fixed at its upper end. A three-way valve controls communication between each of the suction cups either with the atmosphere, or with the vacuum in the inner chamber of the support plate, through a duct formed in the column.
Since the gripping suction cups are installed fixed at the ends of the columns, this type of transport pallet can only contain plane parts. However, parts to be machined are not often plane. Furthermore, the geometric shapes of these parts are frequently different. Therefore, the use of a pallet of this type requires the use of a different gripping device for each part. This is unacceptable in an industrial process due to the cost and times that would be necessary.
Document FR-A-2 711 123 relates to a conveyor-manipulator used for large parts. The equipment comprises two platforms facing each other equipped with a large number of extendible columns fitted at their ends with gripping suction cups installed on ball joints. In this installation, each ball joint is kept in contact with an open ball joint support fixed to the end of the column through an elastic cord. The vacuum controlling gripping in each of these suction cups is applied to a central tube that passes through the corresponding column.
This arrangement can be used to grip parts without a complex geometry due to the movement of the suction cups that is possible due to the way in which they are installed on the ball joints. However, the maximum global movement of each of the suction cups is limited to about 60xc2x0 (+ or xe2x88x9230xc2x0) which is not nearly enough to grip parts with complex geometries.
Based on a layout similar to that described in document FR-A-2 711 123, existing rotatable gripping devices cannot enable global movement of the gripping devices exceeding 80xc2x0 (+ or xe2x88x9240xc2x0) since the vacuum is supplied through a duct that passes through the column and the support in which the ball joint is fitted.
The purpose of the invention is a rotatable gripping device with an innovative design of the suction cup gripping the part providing a global movement of at least 90xc2x0 (+ or xe2x88x9245xc2x0), which enables the assembly of parts with complex geometries that can vary from one part to another with no particular adaptation.
According to the invention, this result is obtained by means of a rotatable gripping device comprising a ball joint, an open ball joint support in which the ball joint can pivot, a device forming a suction cup supported by the ball joint on the outside of the said ball joint support, means of holding the ball joint in the said ball joint support, and a first duct passing inside the means forming the suction cup and comprising at least one orifice formed either on the ball joint or the means forming the suction cup, the said orifice being connected to a flexible tube outside the ball joint support, and that can be connected to a vacuum source, characterized in that the means of holding the ball joint in the said ball joint support comprise a second duct passing through the ball joint support, at least one first orifice of this second duct leading into the space between the ball joint and the ball joint support.
If the vacuum supply to the suction cup passes through a flexible tube connected outside the ball joint instead of passing through a duct inside the column supporting it, the ball joint can rotate significantly further, usually at least 90xc2x0. The device according to the invention is thus adapted to gripping parts with complex geometries, different from one part to the next, with no particular adaptation.
Preferably, the flexible tube connects the orifice in the first duct to a second orifice in the second duct.
In this case, the second duct preferably comprises a third orifice that can be connected firstly to a compressed air source during a phase in which the ball joint is automatically oriented, and to the vacuum source mentioned above during a part gripping phase. With this arrangement, the part can be gripped in a preliminary phase during which the ball joint is automatically oriented with respect to the surface facing the part in order to optimize the orientation with respect to the said surface.
Advantageously, the center of gravity of the ball joint is offset in the opposite direction to the said means forming a suction cup, about a geometric center of the said ball joint. Due to this arrangement, the ball joint automatically returns to a neutral horizontal position when the installation is not in operation.
Preferably, the means forming a suction cup comprises a deformable suction cup and a thrust ring placed inside the suction cup. The presence of the thrust ring causes a better distribution of forces created by the vacuum, which prevents unwanted punching of the part to be machined.
In practice, the ball joint support comprises a spherical cap shaped cavity inside which the ball joint fits. The angle at the center of this cavity is not more than about 90xc2x0.
In order to give a good global distribution of the forces, the diameter of the deformable suction cup is advantageously approximately equal to the diameter of a circle delimiting the spherical cap shaped cavity.
As mentioned above, the ball joint is advantageously capable of pivoting at least 90xc2x0 inside its support.